The present invention relates to a method for making planar waveguides having relatively large thickness dimensions. The invention is useful in fabricating planar waveguide arrays and planar waveguide amplifiers for communications systems.
Optical communications systems can transmit optical signals over long distances at high speeds. An optical signal is transmitted from a light source to a waveguide and ultimately to a detector. Waveguide structures such as optical fibers transmit the light signals. Basically, a waveguide structure comprises an inner core region fabricated from a material having a certain index of refraction, and an outer cladding region contiguous the core comprised of a material having a lower index of refraction. A light beam propagated along the core will be guided along the length of the waveguide by total internal reflection.
Planar waveguides are flat waveguide structures that guide light in essentially the same way as optical fibers. A planar waveguide structure comprises a higher index core strip of material (the xe2x80x9cwaveguide stripxe2x80x9d) embedded in a lower index substrate.
Optical communication systems typically include a variety of devices (e.g., light sources, photodetectors, switches, optical fibers, amplifiers, and filters). Amplifiers and filters may be used to facilitate the propagation light pulses along the waveguide.
The connections between the various system components inherently produce loss in optical communication systems. For example, in planar waveguide amplifiers it would be desirable, to couple planar waveguides with a multimode signal collection fiber. However, applying; conventional processing, planar waveguide amplifiers typically cannot be ma de with cores that are more than about 5 xcexcm thick, and conventional sputtered films have a thickness of about 2-3 xcexcm. On the other hand, a multimode signal collection fiber has a core that is typically more than 50 xcexcm in diameter. This mismatch in vertical dimension makes it very difficult to efficiently couple light from a multimode signal collection fiber to a planar waveguide. Losses can amount to up to 17 dB or in some cases up toxcx9c97 to 98 percent of the transmitted light.
Many other factors also contribute to losses in waveguide connections. Such factors include overlap of fiber cores, misalignment of the fiber axes, fiber spacing, reflection at fiber ends, and the numerical aperture (NA) mismatch. If a fiber receiving light has a smaller NA than a fiber delivering the light, some light will enter the receiving fiber in modes that are not confined to the core and will leak out of the fiber. The loss can be quantified by the formula: Loss (dB)=10 log10 (NA2/NA1)2. Thus, significant losses can occur if fibers are mismatched and signals are traveling from a large core into a smaller core.
With the increasing demand for efficient, large-scale manufacturing of hybrid integrated opto-electronic devices, there is a need to more efficiently couple various waveguide devices together while minimizing losses.
The present invention is a method for making planar waveguides. The method comprises the steps of providing a workpiece comprising a layer of material suitable for the waveguide strip; patterning the layer so that the workpiece comprises a base portion and the at least one protruding portion; forming a cladding layer on the protruding portion; and attaching the cladding layer to a substrate. Depending on the composition of the workpiece, the process may further require removing the base portion. With this method, a planar waveguide or a planar waveguide amplifier may be fabricated having thickness dimensions greater than 5 xcexcm, or more preferably, in the range of 10-20 xcexcm.